<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
async和defer
<script src="a.js" async></script>
<script src="b.js"></script>
<script src="c.js"></script>
<script>
    window.onload = () => {
        console.log('window.onload');
    }

    document.addEventListener('DOMContentLoaded', () => {
        console.log('DOMContentLoaded');
    })
</script>
</body>
</html>